The Medicaid program is a core component of policy efforts to improve the health of low-income children and their parents. However, existing research suggests a puzzle: a large fraction of those eligible fail to participate. Medicaid take-u rates are particularly low for immigrants and children of immigrants, even when they do not face legal barriers to participation. The immediate goal of the proposed project is to understand why eligible immigrants do not participate in the Medicaid program. The proposed study will use randomized field experiments and surveys to evaluate three possible reasons for low program take-up: imperfect information, transaction costs of applying for benefits, and behavioral biases that lead to individuals postponing the application process. There has been little previous work assessing the relevance of these barriers to participation. Thus, it is unclear whether low Medicaid take-up among immigrants is the result of procrastination, a rational response to the complexity of the system, or both. The distinction is important for health policy design, for understanding low program take-up rates more generally, and for identifying domains in which behavioral biases affect human decision-making. The specific aims of the proposed project include: (1) To identify the causal effect of barriers to Medicaid take-up among immigrant populations using randomized field interventions, with a focus on the following barriers: (a) Imperfect information, (b) Transaction costs, and (c) Behavioral biases; (2) To collect detailed information on health insurance status, health care utilization, determinants of Medicaid eligibility, and perceptions of the Medicaid system among a broad sample of 3,600 uninsured legal permanent residents; and (3) To design a future large-scale study quantifying the causal impact of Medicaid participation on health-care utilization and health outcomes. By identifying the empirical relevance of each of the three participation barriers, the study will shed light on te puzzle of low take-up. The research will also produce an evaluation of a five inexpensive, policy-relevant interventions. The most promising of these interventions will be used in a future study to measure the impact of Medicaid participation on health care utilization and health outcomes. Un-insurance is at the top of the national policy agenda, and the 2010 Affordable Care Act aims to dramatically expand coverage. By focusing on immigrants newly eligible for public insurance, the proposed study will inform the effective expansion of health insurance to new populations under health reform.